1) According to categories typical of the philosophy of science, namely, "explanation, reduction and classification."2) The question of how to conceptualize mental illness.3) The relation of mental illness to philosophy of mind, particularly with respect to the tendency of those in the philosophy of mind who illustrate concepts and issues by referring to mental illness.

For the psychiatrist, mental illness represents an abnormality in the brain, which is understood as as much a part of the body as the food or the heart. Some argue that the current DSM model of mental illness is problematic because it contemplates mental illness merely in terms of observable symptoms rather than underlying physiological pathologies, like we do in normal medical science.

A real illness involves observable destrucftion of bodily tissue, and the disease is articulated in terms of this palpable pathology, rather than in terms of abstract concepts with no immediate physiological correlate.

Others, however, are less stringent in their requirements for whether or not something qualifies as a genuine illness. Mental illnesses are instead understood "as collections of symptoms that occur together and unfold in characteristic ways, but it makes no commitments about the underlying causes of mental illness"(Murphy, 2013).

The first set of requirements concerning how to understand mental illness is the "strong" medical model, whereas the latter is the "minimal" medical model. The strong model wants identifiable, pathological processes in the brain. Murphy (2013), however, points out that there is nothing a priori that requires us to think in terms of the strong medical model. Instead, psychiatry is understood as a "multi-level science"(Murphy, 2013).

In addition to the "strong" model, there is also a "minimal" model. This minimal model is agnostic concerning whether or not the medical model of psychiatry commits it to identifying underlying, identifiable, physiological pathologies in the brain.

Diagnostic categories are instead understood in terms of "useful heuristics rather than natural kind terms, whereas a strong interpretation commits psychiatry to a view of mental illness as a medical disease in the strongest sense, that of a pathogenic process unfolding in bodily systems"(Murphy, 2013).

Thte strong interpretation of psychiatry as a medical model may be properly termed neo-Kraepelinian (Murphy, 2013). Kraepelin, who distinguished different forms of clinical insanity, insisted on an understanding of psychiatry as a form of medical science.

Such a picture of mental illness is one in which they "are regularly co-occurring clusters of signs and symptoms that doubtless depend on physical processes but are not defined or classified in terms of those physical processes"(Murphy, 2013).

Murphy further describes the minimalist as one who understands illness, not only mental, but also physical, in terms of a construct whose purpose is to conceptualize a set of symptoms and signs, and that the usefulness of such a construct is that such a constellation provides a route to identifying an underlying biological pathway responsible for the disease.

Indeed, as noted, some thinkers deny that any disease, physical or mental, is a physical process, although it may indeed have consistent physiological bases. Thomas Sydenham, the 17th century English physician, for example, is cited as distinguishing different kinds of pox based on "characteristic courses and outcomes"(Murphy, 2013).

Instead of underlying biological pathways, such a disease model emphasizes observable patterns, prognoses, and phenomena. This is certainly how the DSM understands mental illness, although it contradicts the mainstream medical model which understands illness in terms of physiologically destructive processes.

Murphy points out, however, that others note a fundamental, paradigmatic shift in how medicine is understood by the 19th century. Instead of charting the course of symptoms and outcomes, the emphasis has to do with underlying causes.

Symptoms are traced to underlying biological pathways. The function of psychiatry, in accord with such a model, is not to chart symptoms and courses, but to identify the underlying biological pathways responsible for the observable symptoms. Nevertheless, as Murphy notes, the DSM currently functions according to the minimal, rather than the strong, medical model, in which mental illnesses are "constructs designed to order inquiry"(Murphy, 2013).

This may be understood as a kind of "conventionalist," as opposed to a "realist," conception of disease. Description, statistics, prediction, control and mollifying of the severity of symptoms, is the job of the psychiatrist. For some philosophers of science, Murphy notes, this is all we can hope when it comes to any scientific discipline, and so we ought to expect nothing else from psychiatry.

However, Murphy points out that many scientists are concerned that superficially similar groups of symptoms are being lumped together without respect to underlying biological, or even structural and psychological, differences. Instead, it ought to be the job of the psychiatrist, according to the strong model, to identify the underlying biological pathways responsible for the symptoms.

It is well-known among psychiatrists, for example, that borderline personality disorder is oftentimes confused with bipolar disorder. These two disorders can involve displays of very similar behavioral patterns, yet the underlying psychological and biological pathways are very different. Indeed, Murphy notes that we know from other fields of medicine that a cough, a sore throat, or chest pain, to name only a few examples, can be superficially similar symptoms of otherwise vastly different underlying physiological illnesses.

Murphy notes that while he refers to the DSM approach as neo-Kraepelnian, Kraepelin himself did not see a "construct"-oriented approach to psychiatry as ideal, but rather, as a provisional measure, with the aim of eventually identifying the underlying pathways responsible for the symptoms which we have previously articulated in terms of abstract constructs.

He quotes Kraepelin as saying that “the value of every diagnosis is thus rated essentially by the extent to which it opens up reliable prospects for the future." Kraepelin believed that a physiological approach to mental illness was the ideal, therefore, whereas a conceptual approach was merely provisional. In the words of Murphy, "He considered the correct taxonomy would be one in which clinical description, etiology and pathophysiology coincided."

Murphy notes, however, that we cannot criticize the DSM too harshly for failing to provide the sort of "strong" interpretation of the medical model that we might idealize. This is because its purpose is not to do anything of the sort. Nor does it forbid such a project. Instead, the purpose of the DSM is

"to improve communication between psychiatrists and across disciplines and provide a basis for education. But it is not advertised as the jumping-off point for a mature system of causally organised classification and practice. This reflects a minimal interpretation of the medical model; it can guide empirical research but not uncover causal structure"(Murphy, 2013).

An example of an attempt to replace the DSM construct-model of mental illness would be, in the example of murphy, to replace the construct of pathological gambling with a specific explanation of the behavioral pattern in terms of its underlying biological pathway, which would, in this case, be a dysfunction in the dopaminergic reward system which results in impaired frontal control circuits. This, proponents of the strong model of mental illness argue, would alone be sufficient for a truly medically adequate understanding of psychiatry.

But are we really justified in so optimistic an aspiration? Will we ever be able to develop sufficiently advanced medical equipment that we will be able to identify, in every case, or even in a significant percentage of cases, measurable structural or functional abnormalities in the brains of psychiatric patients?

Perhaps we must perhaps seriously entertain the possibility that psychiatry will never reach the utopian state envisaged by Kraepelin on the grounds that the brain and its vicissitudes are so complex that it is an example of epistemological emergence. From this perspective, there would be no clearly identifiable set of psychophysical laws by which we would be able to readily identify or understand the cause or source of certain psychological problems. Indeed, such a strictly neurobiological approach may be crassly reductionistic, and ignore important psychological and social factors that influence the genesis of mental illness.

It may be a case, to use an example of Jerry Fodor's, of attempting to exhaustively predict and understand economic phenomena purely in terms of the laws of physics. The brain is, after all, the most complicated structural phenomenon known to man. We certainly have no a priori reason to assume that we can exhaustively understand and predict its malfunctions every time.